comments.horne@verizon.net. reliability.dll and glu32.dll should reside in your Windows/System directory.html for the latest program update. For Win95 you will need the Microsoft OpenGL dynamic link libraries (opengl32. Opengl32. CONTACTING THE AUTHOR Programs are only improved by the incorporation of new ideas. currency.
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. This will allow you to view the track of any journey across a high-resolution 3D image of the terrain. mountaineering. or ideas to Richard Horne at r.dll) These file can also be downloaded from the 3DEM home page at http://www. Please report any bugs or send any questions. questions. fitness for a particular purpose.horne@verizon. and GPS tracks produced by the 3DEM computer program are for general visualization purposes only. or visit the 3DEM web page at http://www.net. Less than 512 MBytes of memory will limit the usefulness of the high-resolution modes of OpenGL rendering.com/3dem.visualizationsoftware. Text files of GPS points can also be read and displayed. The user assumes the entire risk as to the results and performance of the 3DEM computer program. GPS referencing. Your ideas are welcome.html.visualizationsoftware. accuracy.EQUIPMENT AND SOFTWARE REQUIRED 3DEM is designed to run under Win95/98//NT/ME/2K/XP or Windows Vista with 24 bit color graphics.dll and glu32. or problem reports are always welcome and should be sent to r. GPS data can be read directly from Garmin and Magellan handheld GPS receivers via a serial data connection to your computer. DISCLAIMER Maps. Comments. three-dimensional terrain images and animations. or other specialized uses requiring high positional accuracy. A minimum of 512 MBytes of memory is also required. 3DEM will display GPS tracks on both the Overhead View and the 3D Scene generated from a Digital Elevation Model. 3DEM is not intended for precise backcountry navigation. No warranty is expressed or implied regarding the use or the results of the use of the 3DEM computer programs in terms of correctness. or otherwise.com/3dem. A one GHz Pentium or better microprocessor and fast graphics card are recommended.

See the description of file types in the section entitled “Digital Elevation Models Available on the Internet”.DIGITAL ELEVATION MODEL FILE SELECTION Choose “File . Each of these selections represents DEM data that are freely available on the Internet.
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Select the File Type that corresponds to the terrain data file that you wish to view.Load Terrain Model” from the Overhead View menu to bring up a dialog box for selection of the type of input data to be used.

SDTS DEM.Resize Overhead View” from the program menu (or use Function Key F6). Just load a new DEM. GTOPO30 DEM. Choose “Operation .LARGE SCALE SHADED RELIEF OVERHEAD VIEW
The first view of any Digital Elevation Model produced by 3DEM is a large-scale shaded relief view of the terrain from directly overhead. A terrain map overlay may also be applied to the shaded relief Overhead View. or Terrain Matrix file. See the instructions under Graphics Overlay Procedure that follow.
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. The lighting angle and depth of shade for the Overhead View can be adjusted by choosing “Color Scale Shaded Relief “from the Overhead View menu. Mars MOLA file. This will bring up the Lighting Parameters dialog box that allows adjustment of the angle and elevation of lighting in degrees and the depth of shade in percent The Overhead View can be resized to larger or smaller scale. Enlarge the Overhead View as necessary to see the desired details in the shaded relief image. GLOBE DEM. and 3DEM will automatically produce an Overhead View. GEOTIFF DEM.

it may be saved as a GeoTiff file that can be used with other Geographic Information Systems applications. If an overlay has been applied to the surface. rescale the Overhead View to a smaller size. Resizing of the Overhead View is useful when a large-scale shaded view of the surface for export to other mapping programs is needed.Convert to UTM” menu item. If errors are present. This will bring up the Map Scale dialog box with controls for selecting the scale of the Overhead View. Choose “Operation . use Adjust Map Overlay Position to make corrections. resize the Overhead View to higher magnifications. it may be interrupted and cancelled using the “Esc” key.Once a large scale shaded relief image has been created.Resize Overhead View” (or Function Key F6) from the Overhead View menu. This allows creation of 3D scenes or flyby animation using very large terrain areas. To obtain high-resolution GeoTiff images. The GeoTiff file contains coordinate information that will allow other GIS applications to accurately position the image in latitude and longitude. Once Overhead View resizing has been started. rescale the Overhead View to a larger size. it is recommended that you resize the map image to a magnification of 2 or more and carefully examine the match between the overlay and the underlying Digital Elevation Model before saving a GeoTiff. and small errors in position may be visible at high magnification.
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.Show DEM Specs” to determine the map projection in use. The Overhead View can be enlarged to maximum size and then saved as an RGB geotiff graphics file format that will be readable by other mapping programs. RESIZING THE OVERHEAD VIEW
Upon loading a DEM or group of merged DEMs. the Overhead View is automatically scaled to fit the entire terrain surface into the available 3DEM window area. The Overhead View can be rescaled to a larger or smaller size by choosing “Operation . The application of the overlay is complex mathematically. To focus on a small area of terrain. Saved GeoTiff images will be sized to match the Overhead View screen display. This function is only available for shaded relief maps that have been created using the UTM map projection. Change the map projection to UTM if necessary with the “File . To move away and use larger areas of terrain.

click the “Save Color File” button to save a colors data file. and adjust its color using the Color Controls RGB sliders. or create a smooth transition (or Spread) between colors at different altitudes.
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TERRAIN COLORS . press the "Spread To" button. click the “Cancel Operation” button. The complete color scale can be saved to a file for future use. Select an altitude using its button in Terrain Colors. Adjust the terrain color scale of the 3D Scene by choosing “Operation .Modify Colors” (or Function Key F3) from the 3D Scene window menu. Once you have defined terrain colors. and then select the desired end point from the altitude buttons to create a smooth transition of colors. press the "Copy To" button.TERRAIN COLORS DIALOG BOX Adjust the terrain color scale of the Overhead View by choosing “Operation .These controls allow selection of terrain color at each of fourteen altitude steps. To copy a color. Colors from this data file can be recalled and applied to the terrain by clicking the “Load Color File” button. choose a starting point from the altitude buttons in Terrain Colors. To spread colors. You can also copy a color from one altitude to another. To cancel the operation to copy or spread colors. The objective is to choose a range of colors to be spread from the lowest to the highest elevation on the surface. and then select the altitude button at the point you wish to copy the color. choose its altitude button in Terrain Colors.Modify Colors” (or Function Key F3) from the Overhead View menu.

It is also possible to modify the low and high elevation limits of the color scale. However. Use the “Store 1.OTHER COLORS . ALTITUDE RANGE . or the text of the scene legend using the Other Colors buttons. You can also modify Other Colors using these sliders. The Color Controls also provide for storage and recall of working color scales as an aide in making fine color adjustments. Click the “Modify” button under “Altitude Range” and enter revised values for the minimum and maximum altitude limits of the color scale. and use the color control sliders to adjust that individual color. Store 2. if you are developing a scene containing the ocean's surface you may want the sea to appear as a uniform ocean color rather than appear as a brightly lighted plane. terrain is a combination of mountains and plains with lighting determined by the azimuth and elevation of the illumination source. you can select the Terrain Type for the 3D Scene from the Terrain Colors Dialog Box. Clicking the “Reset” button will set the altitude limits to the minimum and maximum values found in the entire DEM.You also have the option of adjusting the colors of the sky. You can also use the Island/Ocean setting for scenes in which there are rivers or lakes. Click a Terrain Colors button at an appropriate altitude step.And finally.The Color Controls include horizontal sliders that allow adjustment of the red. This allows choosing a color scale that is precisely matched to the selected terrain area. Recall 1.
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. the ocean. TERRAIN TYPE . the edge of a projection. and Recall 2” buttons to save and recall working color scales to memory while making fine adjustments. and blue components of any individual terrain color. Choose Mountain/Plain for normal scenery. Normally. or Island/Ocean for scenery including the ocean's surface. green. COLOR CONTROLS . Then click the “Apply” button to apply these new low and high elevation limits.

GEOTIFF DEM. large area grayscale heightfield bitmaps for use by other 3D terrain modeling programs. or Terrain Matrix file. Then choose “Color Scale . This will remove all shadows from the image. Rescale the Overhead View to a large size giving high surface resolution. and 3DEM will automatically produce an Overhead View.Modify Scale” from the Overhead View menu to bring up the “Terrain Colors” dialog box. GTOPO30 DEM. load any new DEM.
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. Mars MOLA file. Then choose “Color Scale . To create a grayscale heightfield bitmap. These are Overhead View images in which height is scaled to shades of gray from black at the lowest elevation to white at the highest elevation.Shaded Relief ” from the Overhead View menu. GLOBE DEM. This control will be used to set the color scale from black at the lowest elevation to white at the highest elevation as shown below.GRAYSCALE HEIGHTFIELD BITMAPS 3DEM can produce high resolution. and set “Shade Depth” to zero. SDTS DEM.

Then drag and expand the red outline rectangle around the smaller area that you wish to use and press “Enter. or terrain matrix.Select Smaller Area” (or function key F8) from the Overhead View menu. By merging DEMs and then saving a smaller selected area. custom DEMs can be created that show features that are inconveniently located on the boundaries of published DEMs. choose “Operation . GeoTiff DEM. After loading a large DEM.
This smaller selected area can subsequently be saved as a USGS ASCII format DEM.SELECTING SMALLER GEOGRAPHIC AREA 3DEM allows selection of a smaller geographic area from a large digital elevation model.
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.” 3DEM will then extract this smaller area and display a new Overhead View using the same geographic projection (latitude-longitude or UTM) as the original DEM.

This is particularly true with the SRTM data.Patch Missing Data” from the program menu (or Function Key F7). It will not be suitable for repair of large open-ended areas of missing data such as entire missing valleys or mountain ranges that are sometimes encountered in the SRTM digital elevation models. Choose “Operation . if conversion of the terrain to UTM projection is necessary. and must be patched. which may be sprinkled with obvious holes where elevation values are missing from the terrain grid.
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.” 3DEM will then fill the missing elevation points with values derived from the surrounding area by linear interpolation. Then drag and expand the red outline rectangle to enclose the area that you wish to patch and press “Enter.
Terrain Before and After Patching Missing Data
This patching procedure is suitable for repair of small closed areas of missing elevation data. patching should be conducted before this conversion for most accurate results. Also.TERRAIN PATCHING PROCEDURE Occasionally it will be necessary to patch missing elevation data points in the digital elevation model. These holes can disfigure the 3D images of the terrain.

3DEM will convert then convert the current terrain to UTM projection. below. Terrain data sources such as the NASA SRTM data and the National Elevation Dataset are provided in a geodetic latitude-longitude projection. Areas to be converted must be contained within a single UTM zone.Convert to UTM Projection” from the Overhead View menu.
On the left is a map of Mount Saint Helens in geodetic projection from the National Elevation Dataset. providing a more realistic map view and 3D scene.
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. Also note that conversion to UTM projection can be helpful in application of terrain overlays.Change Projection . The available ellipsoids are WGS84 NAD83 NAD27
There are some restrictions to this conversion. UTM conversions cannot be made for areas that cross zone boundaries or that cross the equator. The UTM projection corrects this distortion. The disadvantage of the geodetic projection is that it introduces an east-west distortion at high latitudes. choose “Operation . UTM zones are North-South strips of 6 degrees longitude in width around the circumference of the globe. On the right is a UTM projection of the same NED data. To convert from geodetic to UTM projections. it may be interrupted and cancelled using the “Esc” key. The map appears stretched in the east-west direction due to the smaller physical distance between longitude points at this high latitude. Converting the terrain to UTM will facilitate matching the terrain and overlay to one another. Once the map projection conversion has been started. An example of this correction is shown in the two overhead (map views) of Mount Saint Helens. Most DRG and DOQ overlays are available in UTM projection using the NAD27 ellipsoid.MAP PROJECTION CONVERSION 3DEM provides the capability to convert any terrain using Geodetic (latitude-longitude) projection into a Universal Transverse Mercator (UTM) projection. Areas to be converted must also be contained between 84 degrees North latitude and 80 degrees South latitude. You will have a choice of ellipsoids to be used for representation of the globe. The east-west distortion has been removed giving a map of the terrain that will match the physical appearance of the surface.

CHANGING UNIVERSAL TRANSVERSE MERCATOR (UTM) ELLIPSOID The UTM ellipsoid defines the shape of the globe used to create those DEMs and GeoTiff overlay files that use UTM projection.Change UTM Ellipsoid” from the Overhead View menu. the ellipsoid of a GeoTiff overlay must match the ellipsoid of the Digital Elevation Model to which is will be applied.Change Projection . you will see an error message “DEM Must First Be Converted to XX Ellipsoid” where “XX” will be one of the ellipsoid choices above. The importance of the ellipsoid here is that all DEMs to be merged must use the same ellipsoid definition. To change the UTM ellipsoid. Any one of the ellipsoids in the table below may be used in common for all DEMs being merged. Choose “OK” and 3DEM will proceed to transform the DEM to the UTM ellipsoid required by the overlay. choose “Operation . Dozens of different ellipsoids have been defined for mapping purposes over the years. Likewise.
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. WGS84 NAD83 NAD27
If you attempt to apply a GeoTiff overlay that uses a UTM ellipsoid not matching the Digital Elevation Model.

Define an area within the Overhead View for conversion into a three dimensional scene.Save Scene Image" from the 3D Scene menu.3D TERRAIN RENDERING PROCEDURE
In addition to the Large Scale Shaded Relief images described previously.Change Position" from the 3D Scene menu (or function key F6). rotate. choose "Operation . rotate.Once you are satisfied with the selected area. Choose "File .View Scene" and 3DEM will give you a choice of terrain projection parameters as explained in the following paragraphs. or shift the position of the landscape relative to the observer. or the Reposition Observer Dialog Box. you can save the image as a graphics file by choosing "File . STEP 3 . Rotate or change the size of the outline rectangle by clicking and holding down the left mouse button at any corner of the rectangle.” Once the scene is complete. STEP 4 . you can just accept the default values and 3DEM will proceed to render the selected projection using OpenGL. 3DEM will then load the selected terrain model and draw an Overhead View of the entire geographic area with color scaled to the altitude at each point on the map. The area to be viewed will be outlined by a black rectangle. To produce a three dimensional scene you must perform four operations in sequence with the 3DEM software as follows: STEP 1 . Choose "Operation . The 3D image will be displayed in a separate window as the “3D Scene. Click the left mouse button at a location on the Overhead View that interests you. Select the file type. compute and display a three-dimensional landscape scene. You can also make fine adjustments to the rotation of the outline rectangle using the left and right arrow keys. 3DEM can also produce oblique angle 3D scenes from any observer position and altitude over the terrain. The observer's location and direction of view are indicated by a notch in one side of the outline rectangle.Load Terrain Model" from the Overhead View menu to bring up the DEM File Type dialog box for selection of the desired file type. or move the scene to obtain the best view of the terrain. Depending on the selected Terrain Position. this will bring up either the Rotate or Shift Scene Dialog Box. Reposition the outline rectangle by clicking the left mouse button at any point of interest on the terrain. These 3D scenes can be used to examine a small section of the terrain or to produce landscape views from the surface of the terrain. These controls allow you to tilt.
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.To reposition the observer or to tilt. STEP 2 . Initially.Load a new terrain file and draw an Overhead View of scaled altitude data. and then locate and open the desired DEM file.

up or down relative to the terrain by use of the “Observer Position” buttons The observer’s look direction can be directed up or down. its position in space or the observer’s position can be modified using fine adjustment controls. giving a choice of scene adjustment as follows:
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. choose "Operation . After rendering a terrain scene. If the Terrain Position is “Background.ADJUSTING OBSERVER POSITION Once a terrain scene has been created. or Fine effect on the observer’s position.Change Position" from the 3D Scene menu (or function key F6).
If the Terrain Position is “Foreground” the Rotate or Shift Scene Dialog Box will appear. left or right by use of the “Look Direction” buttons.” the Reposition Observer Dialog Box will appear. Medium. giving a choice of observer movement as follows:
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Controls can be selected to have a Course. The “Reset” button returns the observer to the initial position used in creating the scene. The observer can be moved forward or back.

Medium. is possible by use of the “Translation” buttons. relative to the observer. is possible by use of the “Rotation” buttons. Rotation of the terrain scene.
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. The Elevation of the terrain scene. can be adjusted up or down using the “Elevation” buttons. The “Reset” button returns the terrain to its original orientation used in creating the scene.• • • • •
Controls can be selected to have a Course. relative to the observer. relative to the observer. or Fine effect on the terrain scene. Translation of the terrain scene.

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. See the descriptions of each parameter which follow.TERRAIN PROJECTION PARAMETERS Terrain projection parameters are selected using this dialog box.

Adjust the legend words to your own preference.LEGEND The Legend is text which will appear at the top of your finished three dimensional scene. The “R/B” or “Red Blue” selection provides a 3D projection for viewing with red-blue lens 3D glasses.. Initially. Legends in Flyby are printed at the bottom of the screen and are only displayed for the first 50 frames of the animation.
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. The type of 3D projection for either single scenes or for flyby projections is determined here. PROJECTION TYPE This control is available from the dialog boxes for Terrain Projection Parameters and Flyby Projection Parameters and is used to adjust the appearance of the final 3D rendering. this legend is read from the DEM file header. The "Color" selection provides a color 3D projection with surface colors determined by terrain height and the direction of illumination. See the illustrations of projection type below. The “S/S” selection provides a side-by-side color stereo 3D projection.

” Using minimum resolution gives the fastest rendering speed while maximum resolution gives the most detailed images possible. while 90 degrees elevation indicates a source directly overhead. Don't hesitate to use magnifications of 200% to 300% to improve the appearance of your scene. OBSERVER’S ALTITUDE The observer’s height above the surface in meters can be set to any value from a high altitude to zero altitude (standing on the surface). 800 by 600. and then make fine adjustments using the Reposition Observer controls. TERRAIN RESOLUTION Terrain image resolution of both the 3D scene and flyby animation can be set to either “Max” or “Min. Thus the default values of 240 degrees azimuth and 60 degrees elevation indicate an illumination source from the southwest. Zero degrees elevation indicates a source on the horizon.
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. and 1024 by 768 pixels. Note that low resolution is always used during real-time View Flyby. It is usually best to create an initial scene using a moderate altitude. These directions are relative to the geographic north at all times.PROJECTION SIZE For 3D terrain rendering and flyby animation. The default value of vertical magnification is 100%. CAUTION – Use of the maximum resolution setting produces the very best 3D images. TERRAIN VERT MAGNIFICATION Large scale DEMs and DTM’s often show very low relief features. you have a choice of projection sizes of 640 by 480. but can require long time periods (sometimes 10 minutes or more) to complete a single scene or animation frame. Experiment with these values if you find a need to change the appearance of light and shadow in your three dimensional projection. while 180 degrees azimuth indicates a source directly from the south. Vertical magnification increases the height of surface features to make them more visible in the three dimensional projection. It is usually a good idea to compose a scene using minimum resolution and then create the final scene using maximum resolution. Maximum resolution during flyby is only available during Animate Flyby. Zero degrees azimuth indicates a source directly from the north. TERRAIN ILLUMINATION OpenGL rendering uses one source of illumination at the azimuth and elevation angles chosen here. Use the maximum resolution setting with caution. but you should change this value if you are not satisfied with the appearance of the 3D projection.

TERRAIN POSITION The position of the terrain model can be chosen to be “Foreground” or “Background” relative to the observer. A Background terrain position will fill the entire display window with a large-scale view of the selected area. Examples of the Foreground and Background terrain positions are shown below.
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. A Foreground terrain position will produce a miniature view of the entire selected area projected into the foreground of the display window.

This situation can result in streaking of the ocean surface or inaccurate rendering of the shoreline when using the Island/Ocean terrain type. or if the shoreline or ocean surface shows rapid flickering during flyby animation. However. If the shoreline is observed to be incorrect. You can also use the "Island/Ocean" setting for scenes in which there are rivers or lakes. the shape of the shoreline may be adjusted by selection of a "Sea Level" value. See the illustrations of Terrain Type below. If you are developing an island and ocean scene.TERRAIN TYPE Normally. if you are developing a scene containing the ocean's surface you may want the sea to appear as a uniform ocean color rather than appear as a brightly lighted plane. use the Lowlands instead of Islands/Ocean terrain type. Choose "Mountain/Plain" for normal scenery.
A variation of the Island/Ocean terrain type called Lowlands is also provided. The Lowlands terrain type provides the best results where large areas of the terrain are very close to sea level. You may need to experiment by raising or lowering the sea level to achieve the proper shoreline or riverbank. or "Island/Ocean" for scenery including the ocean's surface. terrain is a combination of mountains and plains with lighting determined by the azimuth and elevation of the illumination source.
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Animations with smaller projection sizes can be created more quickly. Animations can be created in the following formats. and 1024 by 768 pixels are available. Projection sizes of 480 by 360. Select the file type.Define an area within the Overhead View for conversion into a three dimensional scene. The area to be viewed will be outlined by a black rectangle.Select "Operation .Once you are satisfied with the flight path through space. you may be given a choice of AVI Video Format depending on the capabilities of your machine. Click the left mouse button at a location on the Overhead View that interests you. Reposition the outline rectangle by clicking the left mouse button at any point of interest on the terrain. and can be played back at high speed on most any computer.Load a new terrain file and draw an Overhead View of scaled altitude data. Choose "File . 3DEM will then load the selected terrain model and draw an Overhead View of the entire geographic area with color scaled to the altitude at each point on the map.” and accept the default values of the remaining flyby projection parameters. You can also make fine adjustments to the rotation of the outline rectangle using the left and right arrow keys. The larger sized animations are more impressive to see. whether turning left or right. STEP 3 .Animate Flyby” to create the flyby animation along the flight path previously defined. 800 by 600. you can record a high-resolution flyby animation as either an AVI or MPEG file that can be played back using the Windows Media Player. or diving.Free Flight.3D FLYBY ANIMATION PROCEDURE . If you are given a choice.View Flyby" and 3DEM will give you a choice of flyby projection parameters. Select “Flyby Type . The observer's location and direction of view are indicated by a notch in one side of the outline rectangle. climb. The speed of this animation will depend on the speed of your computer and graphics card. A fast machine will allow a frame rate of up to 30 frames per second. STEP 2 .FREE FLIGHT A flyby animation is a stored series of 3D scenes (or frames) which are played back rapidly in sequence to produce the appearance of a flyby. To produce a flyby animation you must perform four operations in sequence with the 3DEM software as follows: STEP 1 .Load Terrain Model" from the Overhead View menu to bring up the dialog box for selection of the desired file type. choose as large an area as possible. 3DEM will then render a real-time animated view of a flyby of the DEM landscape. climbing. So in order to have a far horizon. STEP 4 . However. rather than a narrow view looking downward.
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. they will take much longer to create and may not play back at full speed on machines without the very best graphics hardware. • • • Conventional color 3D animation Red-blue animation for viewing with red-blue 3D glasses Color side-by-side stereo 3D animation
It is important to select an appropriate projection size for the animation. Use the keyboard arrow keys to turn. Rotate or change the size of the outline rectangle by clicking and holding down the left mouse button at any corner of the rectangle. The primary purpose of this operation is to record a flight path through space over the DEM surface for subsequent conversion into a full resolution AVI or MPEG animation. and memory available. The horizon can be no farther away than the outer edge of the selected area. and then locate and open the desired DEM file. If you choose AVI animation. Note that the horizon distance during flyby is determined by the size of the selected area. 3DEM compresses these frames into either an AVI or MPEG file that can be played back with most any commercial or freeware mpeg animation player. A cross mark cursor at the center of the view indicates your current flyby attitude. and dive. It is often advisable to merge several DEMS together to create a very large area that will allow selection of a far horizon in flyby. the Indeo Video Compressor is capable of producing good animations with large projection size and relatively small file size. 640 by 480. Select “Operation .

3D FLYBY ANIMATION PROCEDURE - GPS TRACKS Flyby animations can also be created to follow GPS waypoints or tracks in position and altitude. These GPS points may be waypoints or tracks downloaded from a handheld GPS receiver, points read from GPS Waypoint or Track Files or IGC Flight Path files, or they may be manually entered on the DEM Overhead View using the mouse. To produce a flyby animation using GPS points, you must perform five operations in sequence with the 3DEM software as follows: STEP 1 - Load a new terrain file and draw an Overhead View of scaled altitude data. Choose "File - Load Terrain Model" from the Overhead View menu to bring up the DEM File Type dialog box for selection of the desired file type. Select the file type, and then locate and open the desired DEM file. 3DEM will then load the selected terrain model and draw an Overhead View of the entire geographic area with color scaled to the altitude at each point on the map. STEP 2 - Enter GPS waypoints or tracks. To load GPS track files, choose “GPS - Transfer GPS Points File to Screen” from the Overhead View menu. Either Waypoint Files or IGC Flight Path Files may be selected. To read GPS waypoints or tracks from a handheld GPS receiver, choose “GPS - Transfer GPS Points - Receiver to Screen” from the Overhead View menu and follow the directions given under GPS Interface. To enter points manually, choose “GPS - Enter GPS Points By Mouse” and then click the left mouse button at each desired point on the DEM Overhead View. STEP 3 - Define the surface area to be included in each frame of the flyby animation. Rotate or change the size of the outline rectangle by clicking and holding down the left mouse button at any corner of the rectangle. Reposition the outline rectangle by clicking the left mouse button at any point of interest on the terrain. This defines the surface area that will be included in the rendering of each animation frame. Note that the horizon distance during flyby is determined by the size of the selected area. The horizon can be no farther away than the outer edge of the selected area. So in order to have a far horizon, rather than a narrow view looking downward, choose as large an area as possible. It is often advisable to merge several DEMs together to create a very large area that will allow selection of a far horizon in flyby. STEP 4 - Select "Operation - Animate Flyby" and 3DEM will give you a choice of flyby projection parameters. Select a Flyby Speed that is appropriate for the GPS track being used. High altitude flights over a large terrain area require high flyby speed (50 meters per frame or more). IGC Flight Path Files usually require lower flyby speed (10 meters per second or less). Accept the default values of the remaining flyby projection parameters, and 3DEM will render a real-time animated view of a flyby of the DEM landscape. The speed of this animation will depend on the speed of your computer and graphics card, and memory available. A fast machine will allow a frame rate of up to 30 frames per second. The primary purpose of this operation is to record a flight path through space over the DEM surface for subsequent conversion into a full resolution AVI or MPEG animation. Note that the creation of the animation file does not take place at actual flight speed. Depending on the complexity of the terrain and the use of graphics overlays, each animation frame might take a second or two to complete. This means that it may take many times the actual flight time to create an animation. An hour or more may be required to create an animation of a few minutes in length. When using IGC Flight Path Files or other GPS flight recordings, it is generally not practical to view or to create an animation of the entire flight path, which could require hundreds of thousands of frames of animation. Each second of animation (30 frames) will require at much as 800 Kbytes of space, depending on the complexity of the terrain. So an animation of a 20 minute flight could require a gigabyte of file space or more. To solve this problem, 3DEM provides the capability to select a smaller section of the flight path for viewing or animation. You will be prompted to select the beginning point and ending point of the flight along the recorded track. Look for further details under IGC Flight Recording.

It is important to select an appropriate projection size for the animation. Projection sizes of 480 by 360, 640 by 480, 800 by 600, and 1024 by 768 pixels are available. Animations with smaller projection sizes can be created more quickly, and can be played back at high speed on most any computer. The larger sized animations are more impressive to see. However, they will take much longer to create and may not play back at full speed on machines without the very best graphics hardware. If you choose AVI animation, you may be given a choice of AVI Video Format depending on the capabilities of your machine. If you are given a choice, the Indeo Video Compressor is capable of producing good animations with large projection size and relatively small file size. You may also choose to create an MPEG-1 animation. However please note that MPEG-1 is limited to a maximum animation size of 640 x 480. MPEG-1 full screen animation is not possible. Use AVI if full screen animation is required.

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3D ROTATION ANIMATION PROCEDURE 3DEM can be used to create a 3D animation of rotation about a fixed point on the terrain surface. STEP 1 - Load a new terrain file and draw an Overhead View of scaled altitude data. Choose "File - Load Terrain Model" from the Overhead View menu to bring up the DEM File Type dialog box for selection of the desired file type. Select the file type, and then locate and open the desired DEM file. 3DEM will then load the selected terrain model and draw an Overhead View of the entire geographic area with color scaled to the altitude at each point on the map. STEP 2 - Define an area within the Overhead View for conversion into a three dimensional scene. Click the left mouse button at a location on the Overhead View that interests you. The area to be viewed will be outlined by a black rectangle. The observer's location and direction of view are indicated by a notch in one side of the outline rectangle. Rotate or change the size of the outline rectangle by clicking and holding down the left mouse button at any corner of the rectangle. Reposition the outline rectangle by clicking the left mouse button at any point of interest on the terrain. You can also make fine adjustments to the rotation of the outline rectangle using the left and right arrow keys. STEP 3 - Once you are satisfied with the selected area, compute and display a three-dimensional landscape scene. Choose "Operation - View Scene" and 3DEM will give you a choice of terrain projection parameters as explained in the following paragraphs. Initially, you can just accept the default values and 3DEM will proceed to render the selected projection using OpenGL. The 3D image will be displayed in a separate window as the “3D Scene.” Once the scene is complete, you can save the image as a graphics file by choosing "File - Save Scene Image" from the 3D Scene menu. STEP 4 - Now choose “File - Save Rotation Animation” from the menu of the 3D Scene menu. Select a file name and AVI animation format as requested, and 3DEM will then create and save an animation rotation consisting of 360 degree rotation in 180 animation frames. It is important to select an appropriate projection size for the animation. Projection sizes of 480 by 360, 640 by 480, 800 by 600, and 1024 by 768 pixels are available. Animations with smaller projection sizes can be created more quickly, and can be played back at high speed on most any computer. The larger sized animations are more impressive to see. However, they will take much longer to create and may not play back at full speed on machines without the very best graphics hardware. If you choose AVI animation, you may be given a choice of AVI Video Format depending on the capabilities of your machine. If you are given a choice, the Indeo Video Compressor is capable of producing good animations with large projection size and relatively small file size. You may also choose to create an MPEG-1 animation. However please note that MPEG-1 is limited to a maximum animation size of 640 x 480. MPEG-1 full screen animation is not possible. Use AVI if full screen animation is required.

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. See the descriptions of each parameter which follow.FLYBY PROJECTION PARAMETERS Flyby projection parameters are selected using this dialog box.

choose here to make these points visible or invisible in the final animation. Experiment with flyby speed during real-time flyby to choose a speed that is matched to the altitude and scale of the terrain below. Ninety degrees terrain angle corresponds to a view looking straight down at the surface. each animation frame might take a second or two to complete. FLYBY ALTITUDE Viewpoint altitude can be adjusted to improve the field of view during a flyby. When viewing a real-time flyby with 3DEM. When following IGC Flight Path recordings or GPS tracks above the surface of the terrain. The initial value will be a high above the landscape surface. An hour or more may be required to create an animation of a few minutes in length. or by following GPS waypoints or tracks. Zero degrees terrain angle corresponds to a view parallel to the surface. altitude is set automatically as dictated by the GPS data. When creating a flyby using GPS waypoints or tracks. and the complexity of the 3D scene. TERRAIN ANGLE Terrain Angle is the angle at which the observer views the terrain. So. the amount of RAM memory available. During Flyby. Depending on the complexity of the terrain and the use of graphics overlays. VISIBLE GPS POINTS When creating a flyby using GPS waypoints or tracks. It will not be possible in all situations to directly view a 3D flyby at full flight speed. Animations created by 3DEM run at 30 frames per second. Note that the creation of an animation file does not take place at actual flight speed. the number of frames will be automatically set by the flyby speed (below) and the length of the flight path.
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. if you choose a flyby speed of 5 meters between each animation frame. the apparent flight speed for the corresponding animation will be 150 meters per second. points read from GPS Waypoint or Track Files or IGC Flight Path files. Animation playback will ordinarily run at 30 frames per second for AVI and MPEG animation. Lower values can be chosen depending on the terrain. FLYBY SPEED Flyby speed is the distance in meters over the terrain between each animation frame. for example. Lower flyby altitude results in a smaller automatic value of terrain angle. These may be waypoints or tracks downloaded from a handheld GPS receiver. the best solution is to create a flyby animation that can be subsequently viewed at a rate of 30 frames per second. The Flyby Projection Parameters show the value of terrain angle for the altitude at the start of the flyby. MAX LENGTH Select here the maximum number of frames to be included in your flyby animation. In these cases. You will probably need large flyby speeds for very high altitude flybys and low speeds for flybys close to the terrain surface. thus allowing for full flight speed.FLYBY TYPE Flyby animation can be created either by free flight over the DEM surface. This means that it may take many times the actual flight time to create an animation. the time between each frame update will be determined by the speed of your graphics card. or they may be manually entered on the DEM Overhead View using the mouse. terrain angle is automatically adjusted based on altitude above the surface.

Then locate and load the DEM tar. STEP 4 . and apply it to the surface of the Digital Elevation Model.Apply/Remove Map Overlay” (or Function Key F4) to bring up the Map Overlay Dialog Box. Overlay maps must be fixed to the geographic coordinates of the underlying DEM.Load Terrain Model” from the Overhead View menu.Locate a source of DEMs and corresponding surface maps that cover the same geographic area at about the same scale.Download the Showshoe Peak SDTS DEM and matching DRG from http://www. convert it into a geo-referenced overlay.” STEP 3 . good matches are the 7.Load the DRG as a map overlay from the Overhead View before creating the 3D Scene. Choose “File . Winzip can be used for this operation. The DEM will be downloaded as a tar. lakes and rivers.gz file from “Digital Elevation Models (DEM) 24 k. Overlay files can be very large (50 to 100 Mbytes). The following instructions will illustrate overlay of Digital Raster Graphics on a Digital Elevation Model using the Snowshoe Peak. To apply a map overlay using the Map Overlay Dialog Box. Choose “Operation . and other features over the 3D terrain image. DEM and matching DRG available at this location. cities. STEP 1 . For the United States. These files can be found under Lincoln County. These overlays can be Digital Raster Graphic (DRG) or Digital Orthophoto Quad (DOQ) files.5 Minute SDTS DEMs and matching DRGs provided by the USGS at http://www. STEP 2 .com/dem/. The result will be a DRG geotiff graphics file (*. 3DEM will read the coordinates of the DRG geotiff file. and processing of overlays can be a very lengthy process.Start the 3DEM program and Load the Digital Elevation Model. Processing of map overlays is not recommended if you have less than 256 Mbytes of RAM or less than a 1 gHz processor. The result will be previewed in the Map Overlay Dialog Box as shown below.gisdatadepot. and choose “USGS DEM” as the File Type.” The DRG will be downloaded as a zip file from “Digital Raster Graphics (DRG) .com/dem/.tif). Montana.gz file from Step 2 above. STEP 5 .
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. take the following steps in sequence.gisdatadepot.24k. Click the “Load” button and select the DRG file from Step 3 above.GRAPHICS OVERLAY PROCEDURE 3DEM allows you to overlay surface maps showing roads.Decompress and extract the DRG graphics file from the downloaded zip file. Montana.

If the overlay preview is acceptable.3D Scene” (or function key F2) to create a 3D Scene of the terrain. if the words “Geo Reference Complete” do not appear in the Map Overlay Dialog Box. Step 7 below will be required. Then click “Enter” to crop the map borders. The cropping tool consists of an outline rectangle with red colored cross marks at each corner.STEP 6 . click the ”Crop Borders” button on the Map Overlay Dialog Box to bring up a magnified map view. It may be necessary to adjust the map overlay coordinates or dimensions slightly to obtain a perfect match. cropping the borders is the easiest method of georeferencing. Examine the resulting image to see that there is a good match between the map overlay and the underlying DEM features. Go to each corner in sequence and adjust the outline rectangle so that it encloses the entire map area.Choose “Operation .
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. STEP 7 . Because of the UTM coordinate system. and you can proceed to Step 8 to create a 3D terrain view. click the “Accept” button and 3DEM will return to the Overhead View of the terrain showing the applied map overlay. See Adjusting Overlay Position that follows. You can manually geo-reference the DRG image either by cropping the map borders so that the DRG image exactly matches the underlying DEM (click “Crop Borders”). To crop the DRG borders.Occasionally you will encounter DRGs that are not true geotiff files and do not include the necessary geographic coordinates. Clicking on a corner cross mark with the mouse designates it as the active (green) corner which can then be moved with either the mouse or the keyboard arrow keys. However. Be sure that your Windows task bar does not cover either the horizontal or vertical scroll bars in this full screen window. even if small areas of the collar remain. STEP 8 . or by manually entering the latitude and longitude coordinates of known points on the map (click “Geo Reference”). Be sure to enclose the entire area of the map. and manual geo-referencing will be required. and if the words “Geo Reference Complete” appear in Map Overlay Dialog Box. the map will appear tilted within the outline rectangle. For most DRGs. This completes application of the map overlay. In these cases the overlay cannot be automatically geo-referenced by 3DEM.

See the parameter descriptions that follow.GRAPHICS OVERLAY PARAMETERS The parameters of the graphics overlay process are selected using the dialog boxes shown below. the Apply Overlays Dialog Box is used to add. the ocean surface.
Once a 3D Scene has been created.
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. remove. crop. and geo-reference surface maps. resize. or modify overlays to the terrain surface. and to accurately position them relative to the underlying DEM and will apply a map overlay to both the Overhead View and the 3D Scene of the terrain.
The Apply Map Overlay Dialog Box is used to load. and the sky.

Cropping of DRG’s is also necessary in order for the overlay map to exactly match the dimensions of the underlying DEM. In this case. Overlays used by 3DEM can be any of nine different graphics file formats of any dimension. However. DRG’s are usually scanned images of paper maps that have a wide border around the useful map area. CROP BORDERS BUTTON Clicking the “Crop Borders” button will initiate tools for cropping an overlay image to remove unneeded borders or other areas.LOAD AND UNLOAD Use the “Load” and “Unload” buttons to choose an overlay or discard an overlay for either the terrain. Then apply the modified overlay image using 3DEM. Be sure to enclose the entire area of the map. REPEAT OR STRETCH Overlays can either repeat many times across a surface. it is best not to use overlays of more than about 10000 pixels in width in order to keep processing time to a reasonable limit.) to the 3D scene. Cropping is particularly useful when using Digital Raster Graphics (DRG) files as map overlays. or replace the colors of the underlying terrain. The “Blend” and “Replace” buttons are used to make this selection. BLEND OR REPLACE Overlays can be applied so that their colors either blend with the underlying terrain. Note that if you plan to use overlays in generating a flyby animation that you must use the stretch option to fix the overlay to the underlying terrain surface. the overlay image will move and flicker from frame to frame during the animation. The cropping tool consists of an outline rectangle with a red colored cross mark at each corner. etc. See the sections on Automatic and Manual Geo-Reference Procedure that follow for more complete instructions. roads. When blending. even if small areas of the collar remain. The overlay you choose will be previewed in the small window above the selection buttons. Because of the UTM coordinate system of the map. The “Repeat” and “Stretch” buttons are used to make this selection.
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. Choose “Stretch” where you have a large overlay image that you wish to apply as a fixed background (such as clouds for the sky or a surface map overlay for the terrain). or sky. In either case. ocean. except for the features that you wish to be visible. GEO-REFERENCE BUTTON Clicking the “Geo-Reference” button will bring up a magnified map view and initiate tools for accurate referencing of the overlay map to the coordinates of the underlying DEM. Clicking on a corner cross mark with the mouse designates it as the active (green) corner which can then be moved with either the mouse or the keyboard arrow keys. the resulting surface is deformed and shaded to match the peaks and valleys of the underlying terrain. it will appear tilted within the outline rectangle. Otherwise. you can modify the overlay image using most any graphics image manipulation program to recolor all areas of the overlay as white. or stretch so that the overlay exactly matches the surface and is only repeated once. boundaries. Press the “Enter” key to complete the cropping process. Click the”Crop Borders” button to bring up a magnified map view and cropping tool. the color white is treated as transparent. Move to each corner in sequence and adjust the outline rectangle so that it encloses the entire map area. Choose “Repeat” where you wish to apply a very fine pattern across an entire surface. This can be useful for the situation in which you wish the overlay to only apply certain features (such as bodies of water.

Most USGS 7. World Files do not contain a complete definition of map projection or coordinates.5’ DEMs and DRGs use the NAD27 ellipsoid. For successful automatic geo-referencing.
•
Warning Regarding Use of World Files (*. and the message “Geo Reference Complete” will appear in the map window. Most DOQs and other satellite photographs use the WGS 84 ellipsoid.tif) containing the needed coordinate information. Unfortunately.jgw) containing coordinate information is present. geo-referencing will be completed automatically. it is most likely due to differences in UTM zone or UTM ellipsoid. the following conditions must be met. then Manual Geo-Reference will be required as described below. GTOPO30 and GLOBE DEMs will require conversion to UTM.5’ DEMs and associated DRGs. Note that NED data. If you observe an obvious mismatch between the overlay and the underlying DEM.jgw) must be present containing the required geographic coordinates.jgw). Digital Orthophoto Quads (DOQs) from the Microsoft Terraserver at http://terraserver. Most of the DRGs available from the USGS are provided as GeoTiff files. SRTM data. Then click the “Accept” button to apply the overlay to the surface of the digital elevation model. Automatic geo-referencing will normally apply for all USGS 7. Missing is any indication of the UTM zone in use or the UTM ellipsoid in use. The Digital Elevation Model and terrain overlay must both be UTM projections contained in the same UTM zone and hemisphere.Apply/Remove Map Overlay” (or function key F4) from the Overhead View menu to load the selected overlay using the Apply Map Overlay Dialog Box. • • The terrain overlay must be a GeoTiff graphics file containing the required geographic coordinates.com/ include *.microsoft. or a that a separate World File (*. This process is completed automatically during application of a terrain overlay. If the needed coordinate information is available in the GeoTiff overlay file. So in order to properly apply an overlay using a World File for geo-reference. or a separate World File (*. They include only the corner UTM coordinates of the terrain and spacing between terrain points. Click the “Load” button and select the appropriate GeoTiff overlay file.
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. provided that the overlay consists of a GeoTiff file (*.com/ or USAPhotoMaps from http://jdmcox. you must be certain that the overlay UTM zone and UTM ellipsoid match the underlying Digital Elevation Model.AUTOMATIC GEO-REFERENCING PROCEDURE Geo-referencing is the process of precisely matching a terrain overlay to the geographic coordinates of the underlying digital elevation model. If the “Geo Reference Complete” message does not appear. The DEM and the terrain overlay must use the same UTM reference ellipsoid.jgw coordinate files and can be automatically geo-referenced by 3DEM. Choose “Operation .

Enter the known decimal values of latitude and longitude of the two points in the text entry box provided and click the “OK” button. Please remember. When you exit from the geo-referencing function. if the overlay file is named “overlay.txt”.Apply/Remove Map Overlay” (or function key F4) from the Overhead View menu to load the selected map using the Apply Map Overlay Dialog Box. These two points must be separated vertically and horizontally to the greatest extent possible. The tools provided by 3DEM allow you to designate these two points on a magnified map image and will then automatically adjust the position of the map overlay as necessary for an accurate match.MANUAL GEO-REFERENCING PROCEDURE After you have loaded a Digital Elevation Model and applied a map overlay. 3DEM will then apply these corrections to the map overlay. the geo-referencing tools in 3DEM can be used to accurately match the position of the map overlay to the underlying DEM. each time you choose to geo-reference this particular overlay file.txt”. you will be given the option of using the stored coordinates again rather than going through the entire laborious geo-referencing procedure.tif” the saved coordinate file will be named “overlay_ref. The geo-referencing tools consist of two moveable cross-mark pointers that can be positioned on the magnified map. Ideally these two points would then be located in diagonally opposite corners of the map. Thereafter.
Position the red marker at any position on the left (west) side of the map. Georeferencing requires that you know the coordinates (latitude and longitude) of at least two points on the map overlay. Choose “Operation . the coordinates that you have entered are saved to a file in the same directory as the chosen overlay file. and the blue marker at any position on the right (east) side of the map.
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. The coordinate file name is the same as the overlay file name (less extension) with an added “_ref. Then click the “Geo-Reference” button. LONGITUDE IN THE WESTERN HEMISPHERE IS NEGATIVE in value. For example.

an alternative procedure is available that allows you to match the overlay relative to the underlying digital elevation model. if the underlying DEM and the map overlay are perfectly matched.0
These relative coordinates are ratios that can be computed using any unit of measure (feet.0 South Coord = 0. then West Coord = 0.0 Width = 1.
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. pixels) that is common to both the DEM and the overlay map. The surface map and the DEM are aligned by specifying the relative coordinates of the southwest corner and the width and height of the map overlay relative to the underlying DEM. meters. west edge of DEM to west edge of map overlay)/(Total DEM Width) South Coord = (Distance.0 Height = 1. south edge of DEM to south edge of map overlay)/(Total DEM Height) Width = (Width of map overlay)/(Total DEM Width) Height = (Height of map overlay)/(Total DEM Height) By definition.ALTERNATIVE GEO-REFERENCING PROCEDURE If you are working with a terrain matrix file in X-Y coordinates. These values are defined as follows:
West Coord = (Distance.

Increases or decreases the width of the overlay (East-West) with respect to the underlying DEM. a map overlay will require fine position adjustment so that it precisely matches the features of the underlying Digital Elevation Model.Adjust Overlay” from the 3D Scene menu (or function Key F5) to bring up the “Adjust Overlay Position” dialog box as shown below. Click “OK” to apply the correction to the 3D Scene. Click “OK” to apply the correction to the 3D Scene.Moves the overlay vertically (North-South) with respect to the underlying DEM. Choose a scene that includes a prominent and identifiable surface feature that can be used for matching the position of the map overlay. Choose “Operation .
First choose a scene area near the southwest corner of the DEM with the observer is looking directly north. These fine controls make it possible to achieve a very precise match between the map overlay and the underlying digital elevation model. Horz Position .
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.
• • • •
Vert Position .ADJUSTING OVERLAY POSITION Often. Adjust the Vert Position and Horz Position controls to match the map overlay to the position of the chosen surface feature. Choose a scene that includes a prominent and identifiable surface feature that can be used for matching the position of the map overlay. Adjust the Height and Width controls to match the map overlay to the position of the chosen surface feature. making small adjustments each time.Increases or decreases the height of the overlay (North-South) with respect to the underlying DEM Width . Because of interaction between these controls. Then choose a scene area near the northeast corner of the DEM with the observer looking directly north. it may be necessary to repeat this procedure several times.Moves the overlay horizontally (East-West) with respect to the underlying DEM Height .

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. Routes (and often tracks) may be stored in your receiver with a designation or name. Then serial data transfer can be established using either COM1 or COM2 serial ports on your computer. 3DEM will connect these points with a solid line in the order in which they appear in the GPS point file. Choose “GPS .GLOBAL POSITIONING SYSTEM (GPS) INTERFACE 3DEM can transfer position data (waypoints. Garmin eMap. or tracks stored in the GPS receiver using the “Receiver to Screen” option. and 1 stop bit. Garmin eTrex Summit. Routes consist of a sequence of selected waypoints between a starting and ending position. no parity. Garmin GPS III+. 3DEM has been tested with Garmin GPS II+. A complete range of GPS point transfers is possible including: • • Receiver to Screen Receiver to File • • Screen to Receiver Screen to File • • File to Screen File to Receiver
3DEM will display waypoints. and Magellan GPS 315 handheld receivers. Magellan receivers must be set up for either 4800 or 9600 baud both at the receiver and at 3DEM. or tracks) to and from Garmin and Magellan handheld GPS receivers via a serial data connection. and then visualize the traveled path on the Overhead View and 3D projection of the terrain. The interface operates with full duplex data transfer using 8 data bits. Waypoints and routes are made up of individual points that have been entered by the user to mark position along a trail. Garmin receivers must be set up for GRMN/GRMN interface using the internal system menu and always operate at 9600 baud. If so. you must enter the designation or name exactly as recorded in the GPS receiver into the “Name” text box in the GPS interface dialog box to allow 3DEM to locate the desired route or track. routes. This allows you to record GPS points during a trek through the wilderness. Tracks consist of the internal track log of the GPS receiver used to plot a smooth track curve on the GPS display.Transfer GPS Points” to bring up the GPS interface dialog box as shown below.
Either a Garmin or Magellan receiver may be selected. routes. Generic interfaces are also provided for other models from these manufacturers.

Map Overlay View” from the Overhead View menu to see the magnified map display. and then transferring these points to the GPS receiver using the “Screen to Receiver” option.The magnified map display available in 3DEM allows plotting of GPS points to a few meters accuracy on an overlay map. or VRML worlds created by 3DEM. 3D flyby animation. Choose “GPS .” and then click the left mouse button to enter GPS points in sequence. 3DEM also provides the option of entering GPS points manually. The maximum number of waypoints that can be loaded into the receiver is 500. Choose “Operation .
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.Enter GPS Points by Mouse. This also allows planning a course or trail with high accuracy. Points transferred to the GPS receiver (Screen to Receiver or File to Receiver) are loaded into the receiver memory as waypoints. and then visualizing it with the 3D Scene.

0 920.0 955.0 871. you must still include an altitude column in the 3DEM track file.32332 -78.longitude .55141 38. Values are in decimal degrees (latitude and longitude) and meters above sea level (altitude). In this case.55147 38.54889 38.55111 38.31712 -78.0 902.0 983.55012 38. Please note that longitude values are negative in the western hemisphere. set altitude equal to “0” for each point.0 904.54953 38.31915 -78.
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.55074 38.55055 -78.0 879.55079 38.54847 38.31562 -78.55140 38.31750 -78.0 984.31773 -78.0 988.0 891.55095 38.55122 38.31449 -78.0 955. However.31251 896.GLOBAL POSITIONING SYSTEM (GPS) TRACK FILES 3DEM stores GPS points as a series of latitude .54794 38. 38. please note that if your GPS data does not include altitude.55159 38.0 972.altitude values in an ASCII text file as shown below.0
Files of GPS points from other mapping programs can be converted into this format using any good spreadsheet program.32410 -78.0 942.31754 -78.32264 -78.32083 -78. and 3DEM will place the GPS track on the terrain surface.0 890.31617 -78. Recorded files can be transferred as waypoints back to either the GPS receiver or to the 3D display generated by 3DEM. Files of this type can be saved from the GPS receiver and from the 3DEM screen display.32195 -78.54888 38.31500 -78.0 881.32408 -78.

also known as the IGC. and an altimeter for measurement of altitude. Choose “GPS . This allows selection of the most interesting section of the flight path for animation. has developed a specification for flight path recording using GPS for measurement of latitude and longitude.IGC FLIGHT RECORDING The Federation Aeronautique International (FAI) Gliding Commission. 3DEM can read and display files of IGC flight paths and thus show the 3D track of a flight over the terrain surface.
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. Because these flight paths can be very long.
Flyby animations can also be created which follow the IGC flight recording as described under 3D Flyby Animation. giving a view out of the cockpit window.Transfer GPS Points . Then choose “Operation . The IGC flight path file format is specified on page 36 of the “Technical Specification for IGC Approved GNSS Flight Recorders” that can be found at http://www.View Flyby” and select “GPS Flight” from the Flyby Projection Parameters. Choose “GPS .File to Screen” to load an IGC track file.fai.Transfer GPS Points .org/gliding/gnss/tech_spec_gnss.igc file of the proper format to read and display a 3D flight path over the terrain.File To Screen” and select an *.asp. controls are provided to select the beginning and ending points for flyby. You will then be presented with controls for moving the starting point (marked with a black cross) and the ending point (marked with a red cross) as shown below.

click and drag with the right mouse button to define a line between two points on the surface. and points of invisibility are plotted in red. The observer and target heights above the terrain surface are independently adjustable. and a target is placed at the right edge or ending point of the profile. These can be either an elevation profile between two points. Setting target height equal to zero creates a plot of the surface visibility along the line from the observer’s position to the target ending position. an elevation profile will be displayed as shown below. An Elevation/Visibility profile shows points of line-of-sight visibility in green and points of invisibility in red. Either an “Elevation Profile” or an “Elevation/Visibility” profile may be selected.
The elevation profile plot shows terrain elevation as a function of distance between the two selected points. When you release the right mouse button. ELEVATION PROFILE BETWEEN TWO POINTS After loading a digital elevation model and creating an Overhead View. As the target moves toward the observer. it is visible or invisible to the observer depending on the peaks and valleys of the terrain. or an elevation profile along a GPS track. The Elevation/Visibility profile is interpreted as follows.TERRAIN ELEVATION PROFILES Two kinds of elevation profile plots can be produced by 3DEM. An observer is placed at the left edge or starting point of the profile. Points of visibility are plotted in green.
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. An Elevation profile is plotted as a continuous green line.

the NED DEMs.5’ SDTS Digital Elevation Models. which can be considerably longer than the horizontal distance between the starting and ending points of the GPS track. An elevation profile along the GPS track will be displayed as shown below. Note on Profile Accuracy Elevation profiles will be most accurate with high resolution DEMs based on Universal Transverse Mercator (UTM) projection. choose “GPS . and the SRTM DEMs will be less accurate.
The horizontal axis of this plot is distance traveled in the horizontal plane.Profile GPS Track” from the Overhead View menu. The vertical axis of this plot is terrain elevation along the GPS track.
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. UTM DEMs preserve the geometry of straight lines on the surface of the terrain. Examples of these DEMs are the USGS 7. Elevation profiles produced using DEMs based on geodetic (latitudelongitude) projection such as the USGS one-degree DEMs. which is important to the accuracy of the terrain profile.ELEVATION PROFILE ALONG A GPS TRACK After loading a digital elevation model and defining a GPS track.

GeoTiff DEMs are a fairly efficient way to save large merged DEMs.
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. Choose “File .tif) graphics files except that instead of color pixel values.tif) file extension. GeoTiff DEMs are similar to Tiff (*. They can only be read by programs such as 3DEM that are designed for their use. and MOLA data must have been loaded as a “Lat/Lon Projection” in order to be saved as a USGS ASCII format DEM. Both GeoTiff and Tiff graphics files use the (*. However. GTOPO30 DEMs. SAVING GEOTIFF FORMAT DEMS Any terrain with geographic coordinates (Latitude-Longitude or UTM) and equal grid spacing between points can be saved by 3DEM as a GeoTiff DEM file. a merged DEM made up of 16 USGS 7. Choose “File . or MOLA data cannot be saved in USGS format.GeoTiff DEM” from the Overhead View menu to save a DEM file in this format.GLOBE.SAVING DIGITAL ELEVATION MODELS SAVING ASCII FORMAT DEMS Any terrain with latitude and longitude coordinates or UTM coordinates and equal grid spacing between points can be saved by 3DEM as a USGS ASCII format DEM file.Save USGS ASCII DEM” from the Overhead View menu to save a DEM file in this format. This provides the capability to load and merge multiple DEMs and save the result as a single USGS ASCII format DEM. the file contains a grid of 16 bit or 32 bit elevation measurements. It also provides the capability to save GeoTiff. GeoTiff DEMs have the disadvantage of not being widely supported by other terrain visualization software. GTOPO30. For example. Note that GLOBE DEMs. However GeoTiff DEMs cannot be read as a graphics file by paint programs. GTOPO30.and MOLA terrain data as USGS ASCII format DEMs for possible use in other mapping applications.5’ DEMs will require approximately 165 Mbytes when saved as a USGS ASCII DEM. Sinusoidal projected GLOBE. Saving the same area as a GeoTiff DEM will require approximately 50 Mbytes.

the ASCII files can be enormous in size and are not recommended unless needed in special circumstances. Choose “File . 3DEM will then read both the terrain matrix file and the associated header file and create the terrain with appropriate map projection and terrain dimensions. 3DEM can then automatically open and read the terrain matrix files without manual entry of any terrain parameters.Entire Terrain” to save the entire terrain area.SAVING TERRAIN DATA FILES Terrain data can be also be saved as terrain matrix files for future use with 3DEM or other applications.5’ SDTS DEMs that are accurate to 0. file_title data_format map_projection ellipsoid left_map_x lower_map_y right_map_x upper_map_y number_of_rows number_of_columns elev_m_unit elev_m_minimum elev_m_maximum elev_m_missing_flag = = = = = = = = = = = = = = OLD RAG MOUNTAIN. Choose “File .
Ordinarily.Selected Area” to save only the area enclosed by the black outline rectangle on the 3DEM Overhead View.Load Terrain Model” and select “Terrain Matrix” file type.
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. when saving data that is known to require fractional accuracy (such as the USGS 7. Below is an example of such a header file. or ASCII text. Each terrain matrix file will be saved with an accompanying text header file that specifies the terrain matrix size. Then select the format of data to be saved as either binary 16 bit integer. VA-24000 float32 UTM Zone 17N NAD27 728530 4264360 739820 4278540 1419 1130 meters 174 1224 -9999
Keep these header files (*.bin).Save Terrain Matrix . coordinate system. However.Save Terrain Matrix . Choose “File . However. binary 32 bit floating point. Data may also be saved as ASCII text for use in special circumstances.1 meter) the binary 32 bit floating point format should be used.hdr) in the same file directory with their matching terrain matrix files (*. and data format. the binary 16 bit integer format is the most compact and useful.

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. Choose “File . this value should be matched to one of the allowable Terragen widths of 256. DEM width from 1536 to 3071 results in Terragen width of 2048. To create Terragen terrain files. 3DEM will export Terragen terrain in widths up to 4096 by 4096 in support of Terragen version 0. etc). DEM width from 768 to 1535 results in Terragen width of 1024. Press the “Ctrl and F8” keys to activate readout of Matrix Width.Save Terragen Terrain .Save Terragen Terrain . If possible.co. 512. To ensure the best reproduction of the terrain surface. 3DEM will then save a terrain *. 512.Selected Area” to save only the area enclosed by the black outline rectangle on the 3DEM Overhead View as a Terragen terrain file.Entire Area” from the Overhead View menu.planetside.uk/terragen/ on the Internet. The rules for dimension matching are as follows: DEM width less than 383 results in Terragen width of 256. Then as the size of the 3DEM outline rectangle is changed. DEM width from 384 to 767 results in Terragen width of 512. load a terrain digital model into 3DEM. the width of the terrain matrix to be converted to Terragen terrain is shown as “Matrix Width” at the bottom right of the Overhead View window. Then choose “File . 3DEM attempts to find the best match between the terrain matrix width chosen in 3DEM and the fixed widths allowed by Terragen (256.8 and higher. 1024. 1024.SAVING TERRAGEN TERRAIN FILES 3DEM can export data files for use by the Terragen terrain-rendering program.ter file which can be opened and displayed by Terragen. Terragen can be found at http://www. or 4096. DEM width greater than 3072 results in Terragen width of 4096. 2048. This terrain will include the entire area of the DEM as seen in the 3DEM Overhead View. Terragen can produce spectacular clouds and atmospheric effects and also provides advanced surface texturing capability. it is advisable to select an area in 3DEM that matches the allowable Terragen widths.

wrl) which can then be viewed and explored in real time over the Internet using a VRML plug-in to your web browser.jpg file. Both of these files are then used by the VRML player to display the world. A value of 45 degrees is normal. The terrain grid defines the surface elevation at each point in the world.snafu. The terrain grid is saved in the *.de/hg/ is highly recommended. World Dimension requires a trade-off between level of detail and the size of the resulting world file. So a VRML world with a dimension of 200 will be made up of almost 80000 faces. Once you have generated a 3D scene choose “File . The GLView player available at http://home. and the JPEG image is saved separately as a *. and the JPEG image is applied as a overlay to define the colors at each point in the world. Then you will be presented with the VRML dialog box for selection of the level of detail in the VRML world. If you plan to use the VRML on a web page. If N is the world dimension chosen. Obviously. 3DEM creates the VRML world by first constructing a terrain grid of elevation values and then by rendering a JPEG overhead image of the selected terrain. but you can choose narrower fields if necessary to improve the appearance of the scene. the number of individual triangular faces making up the VRML world is 2*(N-1)*(N-1).
World Dimension is the number of points per side which make up the VRML terrain grid. be sure that the associated JPEG file is also available and can be located by the VRML player. which will be used by the VRML player. Note that this field of view is independent of the field of view that you have selected within 3DEM for the 3D scene rendering.wrl file. Field of view is the angular field of view.SAVING VRML WORLDS 3DEM can save a 3D scene as a Virtual Reality Modeling Language (VRML) world file (*.
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.Save VRML World” from the 3D Scene menu.

Such large images are often needed for publishing purposes. The size of the printed image will be automatically adjusted to match the size the paper being used.Save Large Format Image” from the 3D Scene menu and choose image size from the Image Parameters Dialog Box that appears. choose “File Save Scene Image” from the 3D Scene menu. Often an image printed at a high value of dots per inch will appear much smaller than on your computer screen. it may be saved as a large format image file of up to 6000 pixels width. Choose “File . Saving large jpeg scenes will sometimes fail if sufficient graphics memory is not available. *.tiff) Both the Overhead View and the 3D Scene can be saved as graphics files.tif. Image magnification is provided as an option where the image is to be printed or displayed in another application.bmp. This will bring up a standard Windows Print Dialog Box for selection of the printer and page setup. SAVING LARGE FORMAT 3D SCENES FOR PUBLISHING Once a 3D scene has been created. To save the Overhead View. To save the 3D Scene. SAVING LARGE FORMAT 2D SCENES FOR PUBLISHING To save the shaded Overhead View as a large format image for publishing.dib) Tagged Image File (*. Use the “Size When Printed” controls to predict the final printed size of your image as determined by magnification and the dots per inch of your printer. or RGB geotiff image.SAVING AND PRINTING SCENE IMAGES 3DEM can save graphics images in the following file formats. resize the Overhead View to maximum and save the resulting image as a bitmap. jpeg. Windows Bitmap (*.Save Map Image" from the Overhead View menu. try saving the large format scene as a windows bitmap. See Resizing the Overhead View. you can send it directly to a printer by selecting “File .Print Scene Image” from the 3D Scene window menu. The 3D image will then be rendered to this scale and saved to the filename that you select.
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. choose "File . PRINTING IMAGES Once you have created a 3D image. *. In this case.

Currently downloads are free. Usually these are both initially offered as ArcGrid format for download. you may also request the BIL format. Area selection is seamless and is not constrained by latitude or longitude boundaries.Select by Rectangle” function and outline the area of interest using the mouse. with some size limitations. These data are suitable for high resolution.usgs. This site is a convenient source of National Elevation Dataset (NED) and Shuttle Radar Topography Mission (SRTM) terrain data for the United States and other limited areas of the world.
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. Click the “View and Download United States Data” to bring up the map for area selection as shown below. 3DEM will be able to read these files as GeoTiff DEMs. If you are downloading SRTM data. and data can be downloaded immediately.gov. The data that can be used by 3DEM will be the National Elevation Dataset (NED) and the Shuttle Radar Topography Mission (SRTM) data. choose the “Download . The advantage of this site is that high-resolution (30 meter and 10 meter) terrain data can be easily located and downloaded for any area of the United States and many other areas of the world.” Now you can click “Download” to retrieve each data set as a TIF file. Once you have found the desired area. Each download site has its own advantages and disadvantages that are summarized below: USGS SEAMLESS DATA DISTRIBUTION SYSTEM The USGS maintains a Seamless Data Distribution System at http://seamless. low altitude 3D terrain scenes. You will then see a “Request Summary Page” that indicates the data available for download for this area.
Use the mouse and the coordinate readouts at the lower left of the map window to select a location and zoom in to the desired area. Then click “Save Changes and Return to Summary.DIGITAL ELEVATION MODELS AVAILABLE ON THE INTERNET Digital Elevation Models can be downloaded at no cost from several locations on the Internet. 3DEM requires the TIF (GeoTiff) data format instead of the ArcGrid format. so click the “Modify Data Request” button and change the requested format to TIF.

5 km (8.tif) graphics files except that instead of color pixel values. Now select the appropriate *. but are constrained to 1/8 degree latitude and longitude boundaries.
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. Using Seamless Data Distribution Files . Then select “GeoTiff DEM” as the DEM File Type and click OK.html.gisdatadepot. USGS 7. Both GeoTiff and Tiff graphics files use the (*. such as 3DEM. 7. Choose "File . County.
The DEMs found here are approximately 13. These DEMs are not seamless.com/dem/demdownload. However this is easily accomplished by 3DEM and usually will take only a few seconds of time.tif) file extension. the file contains a grid of 16 bit or 32 bit elevation measurements.GeoTiff DEMs are similar to (*.5 minute.5 MINUTE DIGITAL ELEVATION MODELS The USGS has designated GeoCommunity as a repository for 10 meter and 30 meter resolution. They can only be read by mapping programs designed for their use. However GeoTiff DEMs cannot be read as a graphics file by paint programs. and Map Name.Load Terrain Model" from the Overhead View menu to bring up the “DEM File Type” dialog box. DEMs are cataloged here by State.tif file and 3DEM will read the DEM file and create the terrain Overhead View. Multiple DEMs can be merged by 3DEM to cover larger areas.4 miles) square.The disadvantage of this site is that all data are available only in geodetic (latitude-longitude) projection and generally must be converted by 3DEM to UTM projection before graphic overlays can be applied. SDTS format DEMs for the entire United States at http://www.

Using SDTS DEM Files .5 minute digital elevation models and topographic maps for the selected county. Select “USGS DEM” as the DEM File Type and click OK.
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. This map can be quickly applied as an overlay to the 3D terrain using the procedure described in Apply Map Overlay. The advantage of this site is that the very highest resolution (10 meter) DEMs can be downloaded free of charge.Load Terrain Model” from the Overhead View menu to bring up the “DEM File Type” dialog box. A fast download service is available for a fee. 3DEM will proceed to decompress and read the file and create the terrain Overhead View.24k These are the 7. and Map name. It is also very convenient to be able to download a matching DRG for the same terrain area.gz file. See Merging DEMs. This means that it will take at least 10 minutes to download the typical 10-meter DEM (3 MBytes) even with the very fastest Internet connection. Then select the DEM *tar. download speeds are limited to about 5 KB/sec for free downloads. and then click the green download button. These provide the very best high-resolution 3D terrain scenes and animation. The 10 meter DEM is the best choice for high resolution terrain scenes. This requires that you have an external index for each state that will allow you to find County and Map names for your area of interest. The disadvantage of this site is that DEMs must be located by State. An inexpensive map index named MapFinder covering all states is available from Digital Data Services. Also. The 10 meter DEM is usually about 3 Mbytes in size while the 30 meter DEM is usually less than 300 Kbytes in size.24k Digital Raster Graphics (DRG) . County. The DRG is a matching topographic map for the selected area. Select either DEM or DRG. you will see a list of available downloads including Digital Elevation Model (DEM) . DRGs will take longer.5 minute SDTS DEM files can be loaded and automatically merged by 3DEM.After selecting the appropriate state and county. Multiple adjacent 7.Choose “File . the DEM selection will result in a choice of two downloads which are the 10 meter resolution and the 30 meter resolution versions of the same terrain. Often.

g. Using SRTM Data Files . Choose "File . choose “File .ecs.nasa.gz” format.3DEM is designed to merge together multiple GTOPO30 DEM files to provide continuous surface coverage of the entire globe. SRTM data are also available in the BIL and TIF format from the USGS Seamless Data Distribution System at http://seamless.Load Terrain Model” from the Overhead View menu to bring up the “DEM File Type” dialog box.gov/products/elevation/gtopo30/gtopo30. 3DEM can read these files directly without the need for file decompression.gov. Then select “SRTM Data” as the DEM File Type and click OK.
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. If you have obtained data in the TIF format. USGS GTOPO30 DEM FILES Global 30 Arc Second Elevation Data Sets consisting of elevation measurements at intervals of 30 by 30 arc seconds (about 1KM) are available for the entire globe from http://edc.gov/srtm/version2/. Using GTOP30 DEM Files .SHUTTLE RADAR TOPOGRAPHY MISSION (SRTM) DATA Shuttle Radar Topography Mission data files for many parts of the world are available in selected sample data sets from NASA and the USGS at ftp://e0srp01u. N37W105 has its lower left corner at 37 degrees north latitude and 105 degrees west longitude. Data are divided into one by one degree latitude and longitude tiles in geographic projection. Digital elevation model data files are designated by a HGT file extension.tar.usgs. choose GeoTiff DEM as the DEM File Type.e. See Merging DEMs. Note that SRTM files frequently contain areas of missing data that appear as holes in the surface of the terrain. Multiple adjacent SRTM files can be loaded and automatically merged by 3DEM.bil or *. and SRTM-3 sampled at three arc-seconds. Now select the *. Small defects of this type can be corrected using the Terrain Patching Procedure.html GTOPO30 DEMs are downloaded in compressed “. File names refer to the latitude and longitude of the lower left corner of the tile .hgt digital elevation model and 3DEM will read the SRTM data and create the terrain Overhead View. SRTM data are distributed in two levels: SRTM-1 with data sampled at one arc-second intervals in latitude and longitude. Then select “GTOPO30 Tile” and you will be presented with the “Area Selection” dialog box for selection of the geographic position and width (in degrees) of the area to be mapped.usgs.Load Terrain Model" from the Overhead View menu to bring up the “DEM File Type” dialog box.If you have obtained data in either the BIL or HGT format.

Once all files have been loaded.bin) and a header file (*. will appear for each file in sequence. 3DEM provides a choice of either “Lat/Long” or “Sinusoidal” map projection when loading GTOPO30 DEMs.hdr).gov/mgg/topo/globe. NOAA GLOBE DEM FILES Global Land One-km Base Elevation (GLOBE) files consisting of elevation measurements at intervals of 30 by 30 arc seconds (about 1KM) are available from http://www. The disadvantage of the Lat/Long projection is distortion at high latitudes. which produces a surface grid corrected for latitude and a more realistic Overhead View and 3D projection. you will receive a terrain matrix file (*.tgz) with dimensions of approximately 40 degrees in latitude and 90 degrees in longitude.Select a geographic location by clicking and dragging the white outline rectangle on the map of world. with the name of the file to be located contained in the title bar.bin) and a corresponding file header (*. The Lat/Long projection produces a rectangular surface grid with equal extension in latitude and longitude. click “OK” and 3DEM will prompt you in sequence to locate and load the GTOPO30 DEM files that are needed to construct the desired map.
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. You can either download complete GLOBE tiles (*. Adjust the width of the selected area in degrees using the horizontal slider control provided.hdr). Using GLOBE Terrain Matrix Files . 3DEM will proceed to draw an Overhead View of the selected area.noaa. You must locate and load each file that is named in the title bar of the file dialog. or you can interactively select a smaller area to be downloaded as a binary terrain matrix (*. See the description of Terrain Matrix Files under Other Matrix File Formats. Once you have selected a geographic area. A file dialog.When you select a subset or smaller area from a complete GLOBE tile to be downloaded.html There are two ways to obtain GLOBE terrain data. If you are creating images at high latitudes. These files can be read directly by 3DEM.ngdc. try the Sinusoidal projection.

A file dialog. 3DEM provides a choice of either “Lat/Long” or “Sinusoidal” map projection when loading GLOBE DEMs. If you are creating images at high latitudes. click “OK” and 3DEM will prompt you in sequence to locate and load the GLOBE tiles that are needed to construct the desired map. 3DEM will proceed to draw an Overhead View of the selected area.
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. Once you have selected a geographic area.
Select a geographic location by clicking and dragging the white outline rectangle on the map of world.Using GLOBE Tiles . 3DEM can be used to merge these tiles together to provide continuous surface coverage of any area on the globe. Adjust the width of the selected area in degrees using the horizontal slider control provided. The disadvantage of the Lat/Long projection is distortion at high latitudes. Then select “GLOBE Tile” and you will be presented with the “Area Selection” dialog box for selection of the geographic position and width (in degrees) of the area to be mapped.Load Terrain Model" from the Overhead View menu to bring up the “DEM File Type” dialog box. try the Sinusoidal projection. which produces a surface grid corrected for latitude and a more realistic Overhead View and 3D projection. will appear for each file in sequence.If you are able to download complete GLOBE tiles. The Lat/Long projection produces a rectangular surface grid with equal extension in latitude and longitude. with the name of the file to be located contained in the title bar. Once all files have been loaded. Choose "File . You must locate and load each file that is named in the title bar of the file dialog.

LIDAR data are generally not free. LIDAR data create such wonderful Digital Elevation Models that the cost involved may be justified. although there are a few sample files available on the Internet.HIGH RESOLUTION LIDAR DATA 3DEM can process high-resolution LIDAR point cloud files to produce Digital Elevation Models and 3D terrain views.
Digital Elevation Model Created from LIDAR Data (one-half meter grid resolution)
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but at the cost of increased processing time.
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. You are also given a choice of the grid resolution of the DEM that will be created from the LAS files.5 meter grid resolution without moving in to a smaller area of interest. Choose "File . You will then be presented with the “LIDAR Terrain Specification” dialog box for selection of the LIDAR returns to be processed and selection of the desired grid resolution for the resulting Digital Elevation Model. The LIDAR point density (points/sq meter) is given for each LIDAR return type. Then choose “Operation . In general. Smaller values result in a higher resolution Digital Elevation Model. 3DEM will examine the list of selected files and determine the types of returns that are available and calculate point densities for each. structures.0 or 1.1.3DEM can process LIDAR data in LAS file format 1. or Bare Earth Returns if this classification information is available in the LAS files. the LAS file format has provision to identify each return as to its sequence number and probable source.5 meter grid resolution should not be attempted for point densities less than about 3 points/sq meter. LAS is a public file format for the interchange of LIDAR data.Load Terrain Model" from the Overhead View menu to bring up the “DEM File Type” dialog box. or the bare earth. The choices range from 0. and the 1. and processing time can be several minutes.5 meter to 20 meter grid resolution.
Each LIDAR pulse can produce several distinct returns from vegetation.Select Smaller Area” (or function key F8) from the Overhead View menu and move in to a smaller area that can be viewed at very high grid resolution. A good strategy for very large LAS files (or groups of files) is to first view the entire area at 5 meter resolution. which has become a nearly universal standard. LAS files can be enormous in size. Although all LAS files do not do so.0 meter grid resolution should not be attempted for point densities less than 1 about point/sq meter. Then select “LIDAR” and use the LAS file selection box to choose one or more LAS files for processing. 3DEM will give you the choice of using All Returns. A 1600 x 1200 computer screen has less than 2 million pixels. so it is impossible to see all the detail on the screen in a 1 km square DEM at 0. the 0.

bin or *. In general.07 4348806. but at the cost of increased processing time. 359936. An example of groups of ASCII points in this format is as follows. Y. and Z values must all be in units of meters. The XYZ point density (points/sq meter) is given for the selected file.78 3DEM will sort through all of the points and create a terrain grid by extrapolation. and the 1.
You are also given a choice of the grid resolution of the DEM that will be created from the XYZ file.Load Terrain Model" from the Overhead View menu to bring up the “DEM File Type” dialog box.00 -25.00 -25.XYZ COORDINATE POINT FILES 3DEM will read files containing groups of XYZ points recorded as either ASCII floating point values (*.13 4348805.75 4348802. Binary values must be double precision (64 bit) floating point XYZ values in sequence. the 0. The choices range from 0. Choose "File . and Z floating point numbers separated by spaces. You will then be presented with the “Terrain Specification” dialog box for selection of the desired grid resolution for the resulting Digital Elevation Model.60 4348805. X.5 meter to 20 meter grid resolution.80 359935.5 meter grid resolution should not be attempted for point densities less than about 3 points/sq meter.50 17. ASCII values must be organized as X.txt) or as double precision binary floating point values (*. Then select “XYZ Point Cloud” and use the file selection box to find the appropriate file.74 359933.74 359935. Y.27 359934.00 18. These files are assumed to contain a cloud of ungridded scattered points.dat).0 meter grid resolution should not be attempted for point densities less than 1 about point/sq meter.
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.28 4348802.50 17. Smaller values result in a higher resolution Digital Elevation Model.

3DEM will automatically merge the needed files as necessary to create a seamless digital elevation model. There are 16 of these image files (*.img).wustl. and 128 pixels per degree. and you will be presented with a “Mars Area Selection” dialog box as shown below. MEGDR 64 Pixels Per Degree The 64 pixel per degree data set is available at http://pds-geosciences. 32. There are 4 of these image files (*. Choose the “MEG 128” or “MEG 64” Topography Data Set and then select a geographic location by clicking and dragging the white outline rectangle on the map of Mars. The filenames specify the latitude and longitude of the NW corner of the included area. 16.wustl. MEGDR 128 Pixels Per Degree The best resolution Mars data are contained in the 128 pixel per degree data set available from NASA at http://pds-geosciences. Using Mars MOLA Files To use MEGDR files with 3DEM.edu/missions/mgs/megdr. 3DEM will automatically merge the needed files as necessary to create a seamless digital elevation model. It is highly recommend that all 16 files be downloaded and copied into a single directory on your hard drive. choose "File . MEGDRs have been produced at resolutions of 4.edu/missions/mgs/megdr.”
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. 3DEM will read and display MEGDR data of 64 and 128 pixels per degree. It is highly recommend that all 4 files be downloaded and copied into a single directory on your hard drive.html in the MEG128 directory. Then click “OK. each beginning with the letters “megt.img).” Each file covers an area of 90 degrees width in longitude and 44 degrees height in latitude.html in the MEG64 directory. each beginning with the letters “megt. Choose “Mars MOLA” as the DEM file type.” Each file covers an area of 180 degrees width in longitude and 90 degrees height in latitude. The filenames specify the latitude and longitude of the NW corner of the included area. Each file is approximately 127 Mbytes in size.Load Terrain Model" from the Overhead View menu to bring up the “DEM File Type” dialog box.NASA MARS OBITER LASER ALTIMETER (MOLA) FILES The MOLA Mission Experiment Gridded Data Records (MEGDRs) are global topographic map of Mars. Each file is approximately 130 Mbytes in size. 64.

” Select this named file and click “Open.img). 256. NASA MARS OBITER LASER ALTIMETER (MOLA) POLAR FILES MOLA MEGDR data is also available separately for the north and south poles of Mars at http://pdsgeosciences. each beginning with the letters “megt.” Each file is 200 megabytes in size or larger. and then select a geographic location by clicking and dragging the white outline rectangle on the map of Mars. The Lat/Long projection produces a rectangular surface grid with equal extension in latitude and longitude.edu/missions/mgs/megdr. The green boundary rectangle indicates the geographic limits of data in the selected POLAR file. try the Sinusoidal projection. The disadvantage of the Lat/Long projection is distortion at high latitudes.
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Adjust the width of the selected area in degrees using the horizontal slider control provided. There are thus 6 of these image files (*.wustl.3DEM will then determine which MEGDR files are required and will present you with a file selection dialog box for locating these files. The first file to be located will be specified in the title bar of the file selection dialog box.img. and 3DEM will then determine which POLAR file is required and will present you with a file selection dialog box for locating this file. Choose the 128. Click “OK”. The title bar will read something like “Locate MOLA MEGDR File megt44n180hb. Usually two or three MEGDR files are required. and as long as they are located in the same file directory you will only have to locate the initial requested file. which produces a surface grid corrected for latitude and a more realistic Overhead View and 3D projection. If you are creating images at high latitudes. Using MOLA POLAR Files To use MOLA POLAR files with 3DEM.Load Terrain Model" from the Overhead View menu to bring up the “DEM File Type” dialog box. choose "File . 256 pixels per degree.” 3DEM will then proceed to read and merge all of the files needed to produce a digital elevation model and draw an Overhead View centered on the coordinates you have chosen. It is highly recommend that all 6 files be downloaded and copied into a single directory on your hard drive. and 512 pixels per degree are available for each pole. 3DEM will automatically merge the needed files as necessary to create a seamless digital elevation model. 3DEM provides a choice of either “Lat/Long” or “Sinusoidal” map projection when loading MOLA files. and you will be presented with a “Mars Area Selection” dialog box as shown below.html in the POLAR directory. Three data sets consisting of 128 pixels per degree. or 512 pixel/degree Topography Data Set. Choose “Mars Polar MOLA” as the DEM file type.

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.hdr of the same name as the matrix data file. as described below.Some matrix data files will fill in missing data points with a fixed value other than zero. grid spacing. Note that if 3DEM finds a header file *. Most data files produced by machines with Intel processors will contain "Little Endian" data in which the least significant byte is first in the data word.
DATA FORMAT AND OFFSET . If you know this value. binary 16 bit integers. it will assume that you are loading a terrain matrix file as described above.The Mars POLAR files are very large and use a corresponding large amount of computer memory. Elevation values can be read as ASCII. 32 bit floating point values (FLOAT 32). Choose “Files of Type . If you encounter a “Not enough memory” error when loading a POLAR file. OTHER MATRIX FILE FORMATS 3DEM can also read and display other matrix data files that are organized as rows and columns of elevation values. try reducing the width of the selected area (as indicated by the white outline rectangle) using the horizontal slider control.Load Terrain Model” from the Overhead View menu. At least 3 gigabytes of RAM is required to process an entire POLAR file at 512 pixels per degree. Also. MISSING DATA . you will be presented with the “Matrix Data Format” dialog box for entry of the number of rows and columns. specify the header size here as "Offset" in bytes. data format. etc) where each row is made up of sequential columns. or South to North. or as text values (ASCII). etc. DATA BYTE ORDER .Specifies the matrix size as number of columns (width) and number of rows (height). enter it here. Choose “File .Specifies the byte order of the elevation data. Sometimes a large negative number such as -9999 is used to distinguish missing data points.Elevation data must be defined as signed 16 bit integers (INT 16). or East to West. row one followed by row two. Column order may be specified as West to East. Elevation values in the file must have been stored sequentially row by row (that is. Otherwise enter zero. Otherwise. and select “Terrain Matrix” to bring up the “Matrix Data Format” dialog box. Other computers (such as the Macintosh) will produce files of "Big Endian" data in which the most significant data byte is first in the data word. Row order may be specified as North to South. if the matrix data file has a header section prior to the start of the elevation data.All Files” and then select the desired matrix data file. or binary 32 bit floating point numbers. You will find topographic data of both types on the Internet. MATRIX DIMENSIONS . and this selection gives you the option of processing both.

Height measurements are normally used for surface terrain and imply that values increase with greater height above the surface. If UTM is selected. The reference ellipsoid must be one of the following designations WGS84 NAD83 NAD27
If reference ellipsoid is not entered.Specifies the unit of measure of elevation data stored in the data matrix (meters or feet). and to degrees for the Latitude-Longitude coordinate system. Depth measurements are normally used for bathymetry and imply that values increase with greater depth below the surface. VERTICAL UNITS . horizontal units can be either meters or feet.3DEM can display matrix data organized as Universal Transverse Mercator grids (UTM).Specifies the coordinates of the southwest and northeast corner of the matrix. For the X/Y coordinate system. the UTM zone number and reference ellipsoid must also be specified.COORDINATE SYSTEM . a default selection of WGS84 will be utilized. Horizontal units will automatically be set to meters for the UTM coordinate system.
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. HORIZONTAL UNITS . or rectangular X/Y grids. These values must be in the same units of measure identified under Horizontal Units defined above.Specifies the units of measure for grid coordinates. SW AND NE CORNER COORDINATES . rectangular Latitude-Longitude grids. Either “Height” measurements or “Depth” measurements may be selected. The UTM zone number can range from 1 to 60 and must be followed by the letter “N” or “S” to specify the northern or southern hemisphere (for example 17N).

See the previous description of GTOPO30 DEMs and GLOBE DEMs.gz or *.
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.” Then you can select multiple terrain matrix files from the common directory to be merged into one Overhead View. highlight each file required using the mouse. Attempting to merge DEMs across UTM boundaries will also result in the error message “DEMs Are From Different UTM Zones. Note that merged DEMs do not always match perfectly at their boundaries since the quality and accuracy of each DEM can vary widely. Choose “File .5 Minute SDTS DEMs in tar-gzip (*tar.” Then you can select multiple SRTM files from the common directory to be merged into one Overhead View. DEMs to be merged must be adjacent to each other. all of the DEMs to be merged must be contained in the same file directory. To select multiple files.” Adjacent NASA Shuttle Radar Topography Mission (SRTM) digital elevation models can be directly merged by 3DEM. Adjacent 3DEM Terrain Matrix Files can also be directly merged by 3DEM. The only limit to the number of DEMs that can be merged is memory in your computer. 10-meter and 30meter resolution DEMs cannot be mixed. Please note that 7.Load Terrain Model” and select “SRTM Data. Place all files to be merged into a common file directory.5’ DEMs cannot be merged across UTM zone boundaries.tgz) format can be directly merged by 3DEM. The only limit to the number of DEMs that can be merged is memory in your computer. To select multiple files. Mixing DEMs of different resolution will result in an error message “DEMs Have Different Grid Resolutions. Choose “File . The only limit to the number of DEMs that can be merged is memory in your computer.5’ DEMs to be merged must be all of the same resolution. To select multiple files.Load Terrain Model” and select “USGS DEM. Choose “File .” Then you can select multiple DEM files from a common directory to be merged into one Overhead View. and then click OK to load all files into 3DEM. You can check the UTM zone of each DEM by selecting “Operation . highlight each file required using the mouse. Place all files to be merged into a common file directory.MERGING DEMS 3DEM provides the capability to merge multiple DEMs to cover a large surface area at high resolution. USGS 7. 3DEM will automatically determine which DEM tiles must be merged to cover the surface area selected. and then click OK to load all files into 3DEM. That is.Load Terrain Model” and select “Terrain Matrix. That is. 3DEM makes the best match possible with the selected DEMs.Show DEM Specs” from the Overhead View menu. For GTOPO30 and GLOBE DEMs.” Please note that 7. highlight each file required using the mouse. and then click OK to load all files into 3DEM.

2.gz.” Next check the “ETM +” box under “Landsat Imagery” and mark “Orthorectified” in the “Require” column. nn20.gz”.” You will then be presented with a listing of the selected photographs from which you may choose to preview and/or download the associated files. and nn10. green.Landsat 7 ETM images consist of grayscale geotiff images recorded in different color bands.tif.gz. Continue to click on the world map to zoom in to a level at which only four or five adjacent photographs covering the area of interest are shown. 2. Select “Landsat 7 ETM Data” from the GLCF web page. Click the “Select Window” icon (at top of the small map window) and then click “Preview and Download.tif.umd.umiacs. Landsat 7 images have a resolution of 30 meters. So the concept is to combine these three separate grayscale images into a single RGB bitmap that can then be used as a terrain overlay in 3DEM. and 1 geotiff files.
The best images to use with 3DEM are the orthorectified Landsat 7 Enhanced Thematic Mapper (ETM+) data. and then select “Map Search. A graphics editing program such as Photoshop or its equivalent will be required to create the overlay bitmap. which makes them suitable as overlays for large-area 3D terrain views with 3DEM. These are gzip-compressed files (*. which contains information about the geographic coordinates of the image. First download the bands 3. Bands 3.edu/data/.tif. and 1 are a reasonable match to red. Images can also be selected by latitude and longitude limits. and blue visible light.met). USING LANDSAT 7 IMAGES .gz) that usually end with the letters “nn30. It is also important to download the small metadata file (*. These are large files of about 30 megabytes each that can be decompressed using Winzip to about 60 megabytes each.
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. Then click on the world map to locate the area of interest.USING LANDSAT 7 IMAGES AS OVERLAYS Landsat 7 images of the earth are available for free download from University of Maryland Global Land Cover Faclity (GLCF) at http://glcf. Landsat images can be easily located and downloaded from this site using a map of the world showing all available images.

The overlay images are extremely large. the beautiful results can be worth the time and trouble. Every image will be a bit different. and the memory utilization and processing time required are a severe test of 3DEM and of your computer. This will be a very large image of perhaps 200 megabytes in size. You can read the original sun azimuth angle from the metadata file. Now load the appropriate digital elevation models into 3DEM to create the 3D terrain surface. Usually some color adjustment is needed after combining. 3DEM will trim the large bitmap file and save a small geotiff overlay file that can be used subsequently without going through the georeferencing procedure again and again. It is also advisable to set the sun azimuth angle in 3DEM to match that of the original Landsat 7 image.
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. Choose “Color Scale . combine them in Photoshop (or equivalent) into a single RGB color image. Then apply the merged RGB bitmap as a terrain overlay. You can use the latitude and longitude coordinates of the lower left and upper right corners of the image as given in the metadata file for manual georeferencing. Manual georeferencing will be required since the RGB image contains no geographic coordinate information. Then save the combined image as a Windows bitmap file. Typically it is necessary to add yellow to the color balance and to increase the image brightness and contrast.Shaded Relief” from the Overhead View window and set the sun azimuth angle to the appropriate value. so some trial and error will be required here to obtain the most realistic looking terrain.After decompression of the three geotiff files. However. Use of Landsat 7 images as overlays in 3DEM is not for the faint of heart.

las and follow the published LAS Format Specification (version 1.txt) or binary floating point (*. it is likely that the graphics card is not properly handling OpenGL rendering. Y. Disable all hardware acceleration or OpenGL acceleration in the display controls.
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.tar. First determine if updated display drivers supporting OpenGL are available for your graphics card. You might experiment with different levels of hardware acceleration to determine which settings are causing the OpenGL rendering failure. 3DEM expects that USGS 7.dem to be recognized by 3DEM.COMMON PROBLEMS FAILURE OF 3D SCENE.com/3dem.visualizationsoftware.gz). 3DEM expects that LIDAR files be named as *. This will bypass the graphics card hardware and allow OpenGL rendering to be performed in software.5 minute SDTS DEMs will be compressed files named *.gz. 3DEM expects that GTOPO30 DEMs will be compressed files named with SW corner longitude and latitude and a *.dll installed.tar.0 or 1. you will receive an error message upon program startup. You can download the missing files from the 3DEM home page at http://www. or if a 3D scene can be generated but terrain overlays cannot be applied.dat or *. a 3D scene that consists of a blank or completely black window.hdr. MISSING Opengl32. Symptoms of this problem can include a program crash when attempting to create a 3D scene.html FILES NOT RECOGNIZED BY 3DEM File extensions must be of the proper type before files will load correctly. Uncompressed USGS ASCII format DEMs must be named as *. Binary values must be double precision (64 bit) floating point XYZ values in sequence Terrain matrix files must be named *.bin). 3DEM expects that XYZ point cloud files be either ASCII (*. or entirely white or grey terrain after application of an overlay.gz file extension (example e020n40.1).dll If your system does not have Opengl32.txt and have an associated header file named *. ASCII values must be organized as X. 3DEM expects that GLOBE DEMS will be files named alphabetically as a10g through p10g.tar. and Z floating point numbers separated by spaces. then go to the Windows Control Panel and select the Display controls. If updated display drivers are not available.bin or *. FAILURE OF TERRAIN OVERLAY If 3DEM cannot generate a 3D scene. Installing updated drivers will usually solve these problems.

then a DRG overlay can be accurately applied. This includes closing other running programs. Windows programs will attempt to use the hard drive as virtual memory. The program will run with only 512 Mbytes of memory.Show DEM Specs” from the Overhead View menu. and the resulting resized bitmap will be saved for subsequent use.com/ generally use the WGS84 UTM ellipsoid as specified in an attached World File (*. When memory is in short supply. DIGITAL ORTHOPHOTO QUAD OVERLAYS DON’T MATCH The Digital Orthophoto Quads (DOQs) from the Microsoft Terraserver at http://terraserver. MEMORY USAGE 3DEM requires a large amount of memory. but 1 Gigabyte is recommended. The DRG map chosen as an overlay should match the coordinate system information shown here.COMMON PROBLEMS (Continued) STREAKED OR INACCURATE OCEAN SURFACE OR OR INACCURATE SHORELINE Rendering a 3D scene or flyby from high altitude where areas of terrain are near sea level can result in streaks in the ocean surface or inaccuracies in the shoreline. This can be particularly annoying in flyby where the ocean surface or shoreline may flicker from frame to frame. use the Lowlands Terrain Type rather than the Island/Ocean Terrain Type to overcome this problem. try raising the sea level a few meters. When this happens to 3DEM. The best remedy for this situation is to take action to reduce the memory shortfall. DIGITAL RASTER GRAPHIC OVERLAYS DON’T MATCH To use DRG’s as overlays. LOADING OVERLAYS TAKES A VERY LONG TIME The time to load and resize large overlays (such as cropped DRG TIF files) may be lengthy (5 minutes or more) depending on the speed of your computer. try reducing the width of the selected area (as indicated by the white outline rectangle) using the horizontal slider control. Often this will remove the streaks or flickering. Note that this restriction means that you cannot ordinarily overlay a DRG topographic map (UTM projection) directly on to a National Elevation Dataset DEM (Lat/Lon Projection). The Mars POLAR files are very large and use a corresponding large amount of computer memory. 512 Mbytes is a practical lower limit. and of course installing more memory. First. DEM and DRG maps that obviously tilt in different directions are an indication of a mismatch due to different coordinate systems. speed of operation becomes very slow. You can read the characteristics of the DEM by selecting “Operation . you must be certain that the underlying DEM and DOQ overlay are actually from the same geographic area (or UTM zone) and that the underlying DEM also uses the WGS84 ellipsoid. and this is normal for 3DEM. However.microsoft. particularly if you are working with large overlay overlays. choosing smaller sized maps. if you first convert the NED DEM to UTM projection. If you encounter a “Not enough memory” error when loading a POLAR file. See Map Projection Conversion.jgw). Resizing must only be done once for each overlay file. you must have a DRG created with the same coordinate system as the underlying DEM. For a proper match. but will require a great deal of patience.
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. If raising the sea level isn’t sufficient. At least 3 gigabytes of RAM is required to process an entire POLAR file at 512 pixels per degree.com/ or USAPhotoMaps from http://jdmcox.

The code for all map projection conversion is derived from GeoTrans v 2. David A. Key to Geophysical Records Documentation (KGRD) 34. The code for gz and tar. National Oceanic and Atmospheric Administration.gov/pub/gis/sdts/dem. and Paula K. The global terrain image used in the Coordinate Selection dialog box for GTOPO30 and GLOBE DEMs was derived from GLOBE Documentation (ver 1.0).. 325 Broadway.A. Version 1. Colorado 80303.3 provided by the National Imagery and Mapping Agency (NIMA).0. Graphics format conversion and animation are provided by the Multimedia Conversion Library by Robert Tibljas and Zeljko Nikolic. available at http://www.0.gromada.html. Sol Katz provided the SDTS to DEM conversion code and contributed the large library of useful GIS utilities at ftp://ftp. Boulder.gz file decompression is derived from Steve Kirkendall’s public domain source code for “untar.S. U.org/download/NIMA. Global Land One-kilometer Base Elevation (GLOBE) Digital Elevation Model. 1999. Documentation.c”.
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.remotesensing.php3.CREDITS The following organizations or persons have provided free software via the Internet which has greatly contributed to the capabilities of the 3DEM program.com/index. Dunbar.blm. GeoTrans can be downloaded from http://www. National Geophysical Data Center. The late Mr. Hastings.